Method for start-up of a continuous catalytic hydrogen producing system



United States Patent C 3,363,987 METHOD FOR START-UP OF A CONTIN- UOUS CATALYTIC HYDROGEN PRO- DUCllNG SYSTEM John C. Hayes, Palatine, IlL, assignor to Universal Oil Products Company, Des Plaines, 111., a corporation of Delaware N Drawing. Filed Mar. 27, 1964, Ser. No. 355,455 4 Claims. (Cl. 23--212) ABSTRACT OF THE DISCLQSURE In a hydrogen producing system wherein a gaseous hydrocarbon stream, such as CH is catalytically decomposed in a reaction zone in the presence of a moving bed of catalyst to produce a H -rich product steam and carbonized particles, and wherein the carbonized particles are transferred to a separate regeneration zone for contact with air to burn and remove carbon from the particles, and wherein the resulting heated regenerated catalyst particles are returned from the regeneration zone to the reaction zone, the method of starting up the system in a manner to prevent carbon deactivation of the catalyst which comprises the steps of preheating the system to an initial temperature level of about 1200 F., then introducing the charge stream into the reaction zone while maintaining catalyst circulation between the reaction and regeneration zones, introducing air into the regeneration zone at a controlled rate providing a CO CO+CO ratio initially less than about 0.50 to 0.60, gradually raising the temperature level in the system to above about 1500 F. while concomitantly regulating air addition to the regeneration zone to provide an increasing CO CO-l-CO ratio and to obtain an ultimate CO CO+CO2 ratio approaching equilibrium and above about 0.80.

The present invention is directed to an improved method for the start-up of a continuous catalytic hydrogen producing system and is particularly concerned with providing a start-up procedure which precludes rapid deactivation of the catalyst.

In conventional catalytic conversion systems, such as those used for catalytic cracking of a gas-oil to produce an improved cracked gasoline stream, it is customary to provide heat control at the reactor by varying the heat of the hydrocarbon feed stream with heat exchanger or preheater means, as well as by varying the rate of circulation of the hot catalyst being recirculated from the regenerator to the reactor. In the catalytic cracking of oils to provide a gasoline yield, the fluidized cracking units tend to run as heat balanced units without much difiiculty since changes in circulation of particles and changes in the coke burning rate may be readily carried out. An increased circulation rate increases coke deposition in the reaction zone and provides more coke for oxidation in the regeneration zone, and, in the reverse situation, a decreased circulation rate decreases coke deposition and heat output from burning coke in the regeneration Zone, with the variation in coke deposition varying al most linearly with the circulation rate of catalyst in the system for a given gas-oil feed rate. The variations in 3,363,987 Patented Jan. 16, 1968 coke laydown or deposition seem to occur by reason of the heavier hydrocarbon components in the charge which readily go to coke and are absorbed by the circulating catalyst particles in the cracking zone, such that it is well recognized in the cracking art that coke deposition and heat balance may be varied by changing the circulation rate. However, in the cracking or decomposition of methane to hydrogen and coke and in contrast to catalytic cracking, a change in circulation rate does not provide a Variation in the carbon laydown rate, and since the operation is highly endothermic and requires a high temperature preferably above 1500 F., it is necessary to utilize to an optimum degree the heat available from carbon made in the reaction zone from the decomposition reaction.

In an optimum continuous moving bed or fluidized particle system for hydrogen product, carbon is gasified and burned under conditions of incomplete oxidation in the regeneration zone to provide for the production of carbon monoxide and carbon dioxide and to effect the heating of catalyst particles for return to the reaction zone whereby the system may operate in a self-sustaining manner. In other words, in contrast to gas-oil cracking, a preferred operation to decompose a methane or hydrocarbon stream to hydrogen and carbon in a reaction zone, free of carbon oxides, there is close control of the regeneration step such that the catalyst is prevented from pass ing to the reactor in an oxidized state, or with occluded carbon oxides.

It has been found that in the operation of a catalytic processing system, as in the catalytic decomposition of light gaseous hydrocarbon to hydrogen and carbon, that the regenerator can be maintained under reducing conditions, with no free oxygen being present in the flue gas stream, and that the carbon dioxide to carbon monoxide ratio within the regenerator flue gas stream can be varied readily, and at will, within certain limitations of carbon deposition on the catalyst particles and with substantially complete carbon gasification in the regeneration zone. Actual control for the operation of the system resides in the maintenance of a given Eo+co ratio for the flue gas stream leaving the regeneration zone.

Generally, the

CO+CO the carbon on the catalyst particles to CO and to preclude the discharge of free oxygen from the regeneration zone and controllably varying such oxygen introduction to inversely vary the carbon level retained on the catalyst particles and directly vary the carbon dioxide to carbon monoxide ratio produced in the regeneration zone.

For example, with generally steady state operating conditions, when the carbon gasification rate is held steady and there is substantially constant CO to CO ratio in the regenerator and carbon level on the catalyst, then a decreased temperature or heat release per unit of carbon gasified can be attained by increasing the amount of CO make with respect to C0 The oxygen to the regenerator can be reduced with carbon being continued to be gasitied at a constant rate by reason of a catalytic effect in the regeneration zone in accordance with the reaction of CO +C+2CO. On the other hand, an increased temperature in the system may be obtained by adjusting the CO to CO ratio to a higher level by controlling the regeneration operation such that increased quantities of carbon dioxide are formed from the oxidation of carbon monoxide which in turn is being formed from the gasified carbon deposition. With heat being controlled, or produced, by the catalytic reaction of carbon dioxide to carbon monoxide, or by the oxidation of carbon monoxide to carbon dioxide, there is thus provided a means to vary the total heat in the system, with the heat being transmitted from the regenerator to the reactor to in turn provide a decreased or an increased heat level therein.

With respect to a system start-up procedure, it is customary to specify a desired CO CO+CO ratio for operation and plant operators tend to attain this ratio as soon as possible after the introduction of the feed gas to the unit, the ratio being adjusted and obtained by varying the rate of air introduction to the regenerator. Unfortunately, rapid attainment of this desired ratio leads to the problem of catalyst deactivation from what is frequently referred to as carbon poisoning or carbon deactivation, where the catalyst appears to become coated with a hard resistant form of carbon that is not gasifiable and removable by exposure to excess oxygen at conventional regeneration conditions.

It is customary with most fluidized or moving bed processing system to use a direct-fired heater for supplying hot preheating gases to circulate through the unit and bring it up to a temperature level where the charge stream can be cut-in and the regenerator then relied upon to supply additional heat to achieve final operational temperatures. Specifically, in connection with a hydrogen producing system, external preheat means must be relied upon to obtain a temperature level of the order of 1200 F. at which time methane can be fed to the reactor and subsequent carbon gasification in the regenerator from carbon deposition utilized to heat the catalyst and in turn supply an increasing temperature level to the reactor. For example, above 1200 F. there is sufficient methane decomposition, with hydrogen production and carbon deposition to produce regeneration heat to raise the temperature level in the system to the preferred operational range of the order of 1600 F.

Where there is a rapid control of CO CO+CO ratio to high levels and minimum CO production in the regenerator, it appears that there is good initial methane conversion even though temperatures do not reach the 00 to 1600 F. desired operational level; however, the good conversion seems to be followed closely with catalyst deactivation and the impossibility of achievement of high conversions unless there is a gradual replacement of the deactivated catalysts with fresh catalyst. Actual carbon poisoning or deactivation is not corrected by subsequently varying the regenerator operation to have excess oxygen.

It is thus a principal object of the present invention to provide a controlled start-up procedure for a fluidized or moving bed catalytic hydrogen producing system, which precludes rapid catalyst deactivation by charging an adequate air supply to the regenerator during the initial conversion period such that carbon dioxide production is not unrealistically low and carbon inadequately removed.

Broadly, the present invention may be considered to provide in connection with the initiation of a continuous hydrogen producing system, wherein a gaseous hydrocarbon stream is catalytically decomposed in a reaction zone in the presence of moving subdivided catalyst particles to produce a hydrogen rich product stream and carbonized particles, the resulting carbonized particles are transferred to a separate regeneration zone for contact therein with a free oxygen containing stream to effect the burning and at least partial removal of carbon from the particles, and heated regenerated catalyst particles from the regeneration zone are continuously returned to the reaction zone to effect the conversion therein, the improved method of effecting a start-up of the continuously operating system and preventing carbon deactivation of the catalyst which comprises, preheating the system and the charge stream to a level of about l200 F. and then effecting an introduction of the hydrocarbon feed into reaction zone along with catalyst circulation between the reaction and regeneration zones to provide hydrocarbon decomposition and carbon deposition on the catalyst, introducing air into the regeneration zone at a controlled rate providing a CO+CO ratio lower than equilibrium for the temperature and pressure levels encountered as the temperature level increases in the system to an operating level, and then effecting a decrease in the rate of air introduction to the regeneration zone to thereby increase the CO-l-CO ratio to approximately the equilibrium ratio.

More specifically, the improved start-up procedure, in accordance with the present invention, shall provide sufficient oxygen or air to the regeneration of the operational system so as to provide a lower ratio than the calculated equilibrium of CO CO-t-CO for each temperature level at the operation pressure, and thus avoid initially high CO levels that are later desired in the operation of the system.

As a guide, the calculated equilibrium CO CO+CO ratios for the burning of carbon in air may be utilized to control the air addition rate to the regeneration zone. The following data in Table I shows the relationship between temperature level and the foregoing carbon oxides ratio, as relating to the stable graphitic form of carbon and being based upon nitrogen dilution in the flue gas of about 79% and a regeneration pressure of about 10 p.s.i.g. A pressure to 20 p.s.i.g. may be employed in the process.

TABLE I Equillbrium Temperature, C O

CO CO+CO ratio for the ditferent temperature levels; however, it ap- CO CO+CO ratios in the regenerator zone flue gases is not readily possible at the lower temperatures. For example, if below 1300 F. a ratio of 0.8 is attempted by restricting air to the regenerator, then carbon will build up on the catalyst and deactivation may result before an operating temperature of 1600 F. or more is reached. This is particularly true if the catalyst has low carbon tolerance. Actually, the various aspects of carbon deactivation are not entirely understood. It is known that under certain conditions of operation, particularly where there has been an initial high build up of carbon, above 6 to 8 percent, and such quantity of carbon is permitted to circulate in the system without at least partial reduction, then there may be a resulting formation of a hard resistant type of carbon which is ditficult to remove and has a poisoning or deactivating eifect on the catalyst activity. It also appears that the catalyst bases of high silica content are more readily deactivated than those with a high alumina content.

In any event, it has been found that a start-up procedure must be carried out to have a low CO content in the regeuerator and then gradually increase the CO CO-l-CO ratio as the plant temperature is raised to the operating level, where the ultimate operating ratio is to be higher than the equilibrium ratio at the gas cut-in temperature.

Example I In one example, where there is to be a start-up of a hydrogen producing operation in a fluidized system utilizing a natural gas charge stream, and catalyst comprising 10% nickel on 95% silica-5% alumina microspherical base, there may be an initial direct fired flue gas heater attached to the unit and hot gases circulated through the reactor and the regenerator along With subdivided catalyst particles until such time as there is a temperature level of approximately 1200 F. Then natural gas charge is introduced into the reactor zone to effect conversion. The 1200 F. temperature is about minimum to have methane decomposition such that there will be hydrogen formation and carbon deposition suflicieut to have the burning thereof in the regenerator provide catalyst heating to in turn raise the system temperature. On the basis of achieving a preferred high CO CO+CO ratio of the order of at least 0.85, the rapid initial control of the air to the regenerator to this ratio in the flue gas stream permits a rapid laydown of coke on the particles as they circulate between the reactor and the regenerator. The initial methane conversion may look quite satisfactory, being of the order of 85% of theoretical; however, after the first few hours of conversion or shortly after an operating temperature level of 1600 F. is reached, maintaining a 10 p.s.i.g. pressure and with a continuing 0.85

CO CO +CO ratio, it is found that conversion begins to fall off. It is also found that a high carbon level exists on the catalyst particles, and that increasing the air rate to the regenerator does not appear to properly reactivate the catalyst. The carbon level may be decreased to what might be an acceptable level while the carbon dioxide level is permitted to increase in the regenerator, but this carbon removal may be slow and hindered by being of a resistant type. Then shortly, with the unregeneratable carbon deactivation condition existing on the catalyst, there is a gradual falling oif of methane conversion and a necessity for adding fresh catalyst to the system or closing down the unit for entire catalyst replacement.

Excess carbon on the catalyst particles can also lead to the existence of local hot-spots within a regeneration zone, as well as give rise to the problem of deactivation.

Example 11 In another example of a start-up of a fluidized hydrogen producing system, there has been effected the initial preheating of a unit to a temperature level of about 1200" F. and the circulation of alumina-silica catalyst particles in the same manner as set forth for Example I. Subsequently, the natural gas charge stream was cut into the reactor to permit methane decomposition and an increased temperature level in the system by burning coke in the regenerator and in turn increasing the catalyst temperature. Air was added to the regenerating zone at a controlled rate providing an initial CO CO-l-CO ratio of 0.5 at the top of the zone. As the temperature level in the unit increased to about 1500 F., and pressure maintained at 10 p.s.i.g., then the CO CO-l-CO ratio was regulated by air out back to be about 0.8. Above 1550" F. and at the operating temperature level of 1600 F. the carbon oxides ratio was maintained at 0.85.

With this start-up, it was found that better than a 91% conversion of the methane was obtained and that no catalyst deactivation was experienced. In fact, with subsequent test runs utilizing the same catalyst, it appeared that the conversion and the hydrogen purity increased slightly.

From the foregoing, it may be observed that there is a definite advantage in utilizing an initial low CO CO+CO ratio for the start-up period. However, it is not intended to limit the procedure to any exact ratio numbers or to temperature levels where the ratio changes, although, in all cases, there must be a ratio lower than the equilibrium ratio for the particular temperature level.

It may also be pointed out that start-up temperature levels, for hydrocarbon feed cut-in, will vary in accordance with the facilities available for preheating the conversion unit. For example, with pilot plant units, it may be possible to effect preheating to high levels of the order of 1350 F. to 1400 F. such that somewhat higher initial CO CO+CO ratio of the order of 0.80 could be used. However, with a large commercial unit, it may be difiicult or expensive to elfect preheating above the minimum at which catalytic methane decomposition will take place, such that an initial low carbon oxides ratio is preferably used and temperature increased in the system by raising the catalyst temperature in the regenerator with carbon oxidation.

I claim as my invention:

1. In the operation of a continuous hydrogen producing system wherein a gaseous hydrocarbon stream is catalytically decomposed in a reaction zone in the presence of moving subdivided catalyst particles to produce a hydrogen rich product stream and carbonized particles, the resulting carbonized particles are transferred to a separate regeneration zone for contact therein with a free oxygen containing stream to effect the burning and at least partial removal of carbon from the particles, and heated regenerated catalyst particles from the regeneration zone are continuously returned to the reaction zone to effect the conversion therein, the improved method of effecting a start-up of the continuously operated system and preventing carbon deactivation of the catalyst which comprises, preheating the system to an initial temperature level suflicient for catalytic methane decomposition, and then eiiecting an introduction of the charge stream into the reaction zone along with catalyst circulation between the reaction and regeneration zone at a controlled rate precluding an excessive carbon build-up on the catalyst and to provide a CO CO-i-CO ratio initially less than about 0.50 to 0.60, thereby effecting an increasing catalyst temperature and conversion temperature level in the system, and then incrementally decreasing the air addition to the regeneration zone responsive to temperature level increases in the system While correspondingly increasing said ratio to obtain a predetermined desired operating temperature level higher than said initial temperature and an ultimate CO CO-l-CO ratio that approximates the equilibrium ratio and is. above about 0.80, whereby a high CO content and re-- ducing atmosphere is maintained in the regenerating zone..

2. In the operation of a continuous hydrogen producing system wherein a gaseous hydrocarbon stream is catalytically decomposed in a reaction zone in the: presence of moving subdivided catalyst particles to: produce a hydrogen rich product stream and carbonized particles, the resulting carbonized particles are transferred. to a separate regeneration zone for contact therein with. a free oxygen containing stream to effect the burning and at least partial removal of carbon from the particles, and heated regenerated catalyst particles from the regeneration zone are continuously returned to the reaction zone to effect the conversion therein, the improved method of effecting a start-up of the continuously operated system and preventing carbon deactivation of the catalyst, which comprises, preheating the system to a level of about 1200 F. and then effecting an introduction of the charge stream into the reaction zone along with the catalyst circulation between the reaction and the regeneration zones to provide hydrocarbon decomposition and carbon deposition on the catalyst, introducing air into the regeneration zone at a controlled rate providing a CO co-lrco ratio initially less than about 0.50 to 0.60, gradually rais- 8 'ratio which approaches equilibrium and is above about 0.80.

3. The method of claim 2 further characterized in that with the regeneration zone pressure is maintained in the range of from about 10 p.s.i.g. to 20 p.s.i.g. and after the temperature of said system reaches above about 1350 F., the amount of air is reduced to provide a CO +CO ratio of above about 0.80.

4. In the operation of a continuous hydrogen producing :system wherein a gaseous methane stream is catalytically decomposed in a reaction zone in the presence of moving subdivided supported nickel catalyst particles to produce a hydrogen rich pro-duct stream and carbonized particles, the resulting carbonized particles are transferred to a separate regeneration zone maintained under a pressure of l020 p.s.i.g. and contacted therein with a free oxygen containing stream to burn and at least partially remove carbon from the particles, and the resulting heated regenerated catalyst particles from the regeneration zone are continuously returned to the reaction zone to effect the conversion therein, the improved method of ei'fecting a start-up of the continuously operated system and preventing carbon deactivation of the catalyst, which comprises, preheating the system to a temperature level of about 1200 F, then introducing the methane charge stream into the reaction zone along with catalyst circulation between the reaction and the regeneration zones to provide hydrocarbon decomposition and carbon deposition on the catalyst, introducing air into the regeneration zone at a controlled rate providing a co co+co ratio initially less than about 0.60, gradually raising the temperature level in the system to an operating temperature level above about 1500 F. to 1600 F, while concomitantly regulating air addition to the regeneration zone to provide an increasing CO CO+CO ratio and to obtain an ultimate CO CO+CO ratiso which approaches equilibrium and is above about 0.8

References Cited UNITED STATES PATENTS 3,129,060 4/1964 Pohlenz 232l2 3,194,636 7/1965 McEvoy 23-2l2 MILTON WEISSMAN, Primary Examiner.

EDWARD STERN, Examiner. 

